1. Field of the Invention
The present invention relates to an image pickup apparatus capable of picking up and recording a still image at high speed without using an interruption routine.
2. Related Background Art
A method of using an interruption function of a CPU in a microprocessor has been proposed for sequence control of a camera system. With this method, as the shutter is half depressed and switch SW1 is turned on, the microprocessor checks a disc drive and a lens, calculates photometry and automatic exposure, displays information in a finder and performs other operations. The calculated photometry and automatic exposure are temporarily stored in a provisional memory and transferred to a regular memory after an interruption is inhibited. Thereafter, the interruption is enabled to repeat an operation of checking the depression of switch SW1. During this loop, if an interruption occurs due to the depression of switch SW2 triggering a shutter release, the microprocessor enters in the interruption routine to initiate the release sequence and pick up an image using the information in the regular memory.
With this method, however, the sequence control jumps to the interruption routine and an image is picked up, even if a lens stop value changes due to zoom adjustment during the loop operation, or without completing the photometry. In such a case, a correct exposure cannot be obtained.
Further, the provisional and regular memories are required because of the interruption process. Thus, the memory capacity becomes two times larger than that without the interruption process, and the program becomes complicated.
A method for the sequence control without the use of interruption function may be possible. With this method, however, an image pickup sequence can be carried out only after various data such as photometry and lens data are collected, thus leading to a time lag between the depression of the release switch and an actual image pickup.
There is known a silver salt SLR camera of a type in which automatic exposure (AE) information is produced for each frame during a single frame photographing mode, and is fixed during a high speed continuous photographing mode (e.g., refer to Japanese Patent Unexamined Publication No. 143218/1978).
The reason why the AE information is fixed during the high speed continuous photographing mode, is that AE sensors are generally mounted within a TTL (Through the Taking Lens) optical path and a quick-return mirror is maintained set up so that light is not incident to the AE sensors.
In contrast, there is also known a video camera as disclosed, for example, in Japanese Patent Unexamined Publication No. 78925/1976, wherein color sensors for detecting R and B (G) color temperatures are mounted on a video camera body. An output ratio between the color sensors is calculated to form color temperature information based on which the color balance of the color signal processing circuit of the camera is adjusted.
An image pickup apparatus such as an electronic still camera adopting the above video camera technique picks up one frame and stores it in a medium such as a magnetic disc. In addition to this fundamental mode, a continuous photographing mode will become necessary for some cases.
With the image pickup apparatus of this type, the output of the color temperature sensor can be always obtained independently from image pickup control, stop control and the like. However, during a high speed continuous photographing mode, there is a problem that the color temperature changes at the frequency two times higher than the commercial power frequency due to flicker phenomenon of a fluorescent lamp. Thus, color changes for each photographed print. This color difference is not so conspicuous for plural prints photographed at relatively low speed, but becomes conspicuous for those photographed at high speed, e.g., 10 frames per second.
To drive a recording or reproducing apparatus with an image pickup apparatus such as a video camera, a battery and an AC adapter have been used selectively.
If a battery having a capacity maintaining a sufficient voltage during large current discharge is used, e.g., if a Ni--Cd battery is used, a motor can be started rapidly. However, if an AC adapter is to be used for the purpose of long time, indoor image regeneration or recording, a large capacity of an AC adapter is needed for large current discharge, and hence it becomes expensive. If an AC adapter of small capacity is used for large current discharge, the voltage will become low and a malfunction may occur.
Electronic apparatus such as an electronic camera often use a battery for their power supply. In this case, the voltage will become low as large current flows for a long time, especially at the end of battery discharge and at low temperature. For this reason, several motors or the like in the electronic camera are driven in such a manner that power consumptions (or peak power consumptions) of these devices do not occur at the same time.
However, this drive operation is sequential in time so that there arises some problems of long time image pickup and record operation, long time release stand-by, large release time lag, long return time of a quick-turn mirror for a single-lens reflex camera, low frame speed for continuous photographing, and the like.
There is known an image pickup apparatus of the type in which gains of color signal passages in a signal processing circuit are automatically adjusted by photographing a white object and making the obtained color signal levels equal to each other.
There is also known an image pickup apparatus of the type in which a plurality of color sensors for receiving light from an object are mounted outside of a TTL optical path. The outputs of the color sensors are compared to calculate color temperature information. The gains of color signal passages from the image pickup elements are always controlled based on the color temperature information.
With the former image pickup apparatus, initial setting for white balance is cumbersome. With the latter image pickup apparatus, an electronic camera is constructed of a shutter, a quick-return mirror, a stop and the like which devices are driven every time a trigger is initiated. Such an electronic camera is associated with a problem that too large a time is necessary for image photographing and recording after triggering operation. Particularly, a microcomputer is generally used for giving various functions to an electronic camera and controlling various devices of the camera. Complicated operations in various modes are executed after the triggering operation. Therefore, if the white balance control operation periodically reading the color sensor outputs is inserted between various sequential operations, the final image photographing and recording operation is delayed thus taking a long time for one frame image pickup.